JPH0587623A - Isothermal control type calorie meter - Google Patents

Abstract

PURPOSE:To enable the shortening of measuring time as a whole by reducing time required for isothermal control by a isothermal control type calorie meter. CONSTITUTION:An isothermal control type calorie meter is made 111 of a photodetecting section A which has a light absorbing body, a heater, a cooling means and a temperature detector covered with a heat insulating jacket and a body part B which has a control section 2 and 3 to control so that a heater 4 is driven based on temperature detection signals from the temperature detectors 6 and 6a to keep the temperature of the photodetecting section A constant and an incident light power calculation means 25 to calculate an incident light power from a difference of the power applied to a heater 4 depending on whether the incident light exists or not. The gain of the control section 23 is changed according to the presence of the incident light or the size of a control deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isothermal control type calorimeter for measuring the power of light such as a laser,
More specifically, it relates to intermittent control of incident light.

[0002]

2. Description of the Related Art As an isothermal control type calorimeter of this type, the one shown in FIG. 6 is well known.

In the figure, reference numeral 1 denotes a heat absorber forming a sensor portion S, which is composed of a heat transfer plate 5 in which a cylindrical body 3 having an inner surface coated with a light absorbing paint 2 and a heater 4 are embedded. Reference numerals 6 and 6a denote temperature difference detecting elements, and 7 denotes a thermoelectric cooling element. These elements are formed of Peltier elements having the same performance and are fixed in a state of being sandwiched between the heat transfer plate 5 and the reference jacket 8. .. The outer circumference of the reference jacket 8 is surrounded by an intermediate jacket 9 and an outer jacket 10 as shown in FIG. 8 in order to stabilize the temperature, and the sensor unit S is configured as a light receiving head A surrounded by a triple jacket. ing. The heat capacity of the heat transfer plate 5 including the tubular body 3 and the heat capacity of the reference jacket 8 are about 1: 1000, and the quasi-jacket 9 is larger.

Reference numeral 11 is a constant current source connected to the thermoelectric cooling element 7. Reference numeral 12 is an amplifier that amplifies the output from the temperature detecting elements 6 and 6a. This output is input to the filter 13 and the voltmeter 16, and the output signal of the filter 13 is input to the adder 14. On the other hand, the output from the voltmeter 16 passes through the arithmetic unit 17 and the programmable power supply 18 and then the adder 14
Is input to and added to the output from the filter 13, and the output is output to the heater 4 through the square root calculator 15.
Reference numeral 19 denotes a digital voltmeter, which measures the voltage V _H applied to the heater 4 and returns the measured value to the arithmetic unit 17. These circuit portions form a main body B for the light receiving head A.

In the above structure, the measurement light is input.
If not, the reference jacket 8 is at room temperature and the Peltier element is
In the thermoelectric cooling element 7 composed of a child, a constant current source 11
Value I _AIs constantly applied to cool the heat transfer plate 5 side.
ing. In this case, the reference jacket 8 side must be heated.
However, the heat capacity of this reference jacket 8 is large,
Since the heating amount of the thermoelectric cooling element 7 is small, the reference jacket
It does not reach the point of raising the temperature of g.

Therefore, in the apparatus shown in FIG. 6, the thermoelectric cooling element 7 and the constant current source 11 constantly act to increase the temperature on the reference jacket 8 side and decrease the temperature on the heat absorber 1 side.

On the other hand, the temperature difference detecting elements 6 and 6a detect this temperature difference (nV level), and the amplifier 12 amplifies the output to (mV level) and outputs it to the filter 13 and the digital voltmeter 16. After removing the noise (high frequency) component, the filter 13 adds the signal V _f to the adder 14
Output to. Temperature difference measured by digital voltmeter 16
P is added to the arithmetic unit 17 and subjected to a predetermined arithmetic operation (this arithmetic operation is a known arithmetic operation for controlling so that the temperatures of the heat transfer plate 5 and the reference jacket 8 coincide with each other quickly), and then the arithmetic value thereof. Is applied to programmable voltage source 18. Output V of programmable voltage source 18 based on this calculated value
_p and the output V _f from the filter 13 are added by the adder 14 and added to the square root calculator 15, where (V _p + V
_f ) 1/2 calculation is performed. The output of the square root calculator 15 is applied to the heater 4 to raise the temperature of the heater 4 and control the outputs of the temperature difference detecting elements 6 and 6a to zero.

Therefore, in the apparatus of FIG. 6, the thermoelectric cooling element 7
With respect to the heat transfer plate 5 cooled by the action of the constant current source 11, a voltage (current I) is applied from the square root calculator 15 to the heater 4 to heat the heat transfer plate 5, and the temperature of the heat absorber 1 and the reference The temperature of the jacket 8 is controlled to match.

In such a state, the laser light L to be measured
_{When a} is incident from the upper part of the cylindrical body 3, the heat absorber 1 absorbs light, and the temperature rises according to the light power. The heat is conducted to the heat transfer plate 5, and a temperature difference is generated between the heat transfer plate 5 and the reference jacket 8 which are in a temperature equilibrium state. The temperature difference detecting elements 6 and 6a detect the temperature difference, and the square root calculator 15 reduces the voltage value sent to the heater 4. Therefore, the temperature of the heater 4 decreases, and the temperatures of the heat transfer plate 5 and the reference jacket 8 become equal again.

By the way, the parts up to the amplifier, filter and square root calculator shown in FIG. 6 can be analog-controlled by PID. By doing so, the number of constituent elements can be reduced, and the cost of the device can be reduced.

When PID control is used, P (proportional), I
Although it is necessary to determine the respective constants of (integration) and D (differentiation), the response time constants of the photodetection section (light absorber, temperature detection element) vary depending on the individual. Therefore, the PID constant is adjusted for each detection unit, or a PID constant that is insensitive to the detection unit time constant is selected.

However, in the method of adjusting the PID constant for each detection unit, the independence (compatibility) of the photodetection unit and the processing unit (hereinafter referred to as the main body) including the PID and the like is lost,
It limits the system's potential for development. In the method of adjusting the PID constant that is insensitive to the time constant of the detection unit, the PID constant (critical braking condition) that minimizes the response speed cannot be used, and thus there is a problem that the measurement time is delayed.

Therefore, the applicant has an isothermal control type calorie capable of performing isothermal control with a minimum response time by an optimum PID constant according to the time constant peculiar to each photodetecting section without impairing the compatibility of the photodetecting section. Japanese Patent Application No. 3-4025 (hereinafter referred to as a prior art) has applied for a meter. This precedent is
The photodetector is configured to be replaceable with the main body, and storage means for storing an optimum PID constant or information for calculating the PID constant is provided for each detection portion. Alternatively, the information for calculating the PID constant is read, the PID constant is set, and the isothermal control is performed by the PID control.

FIG. 7 is a configuration diagram of a prior art example, FIG. 8 is a configuration diagram of a main part of FIG. 7, FIG. 9 is an explanatory diagram of a measurement state, and FIG. 10 is a timing chart showing an operation at the time of measurement. First, the operation of the entire apparatus will be described with reference to FIGS. 9 and 10. In FIG. 9, it is assumed that the laser light output from the stabilizing light source D enters the light receiving head A through the attenuator E and the shutter F.

In the first step of the measuring operation, the shutter F is closed and no light is incident on the light receiving head A. In this state, the heater power _Ph is controlled so that the reference jacket 8 and the heat absorber 1 are in thermal equilibrium. The heater power P _h at this time is P ₀ .

In the second step, the heater power P _h is controlled so that the reference jacket 8 and the heat absorber 1 are in thermal equilibrium with the shutter F open. The heater power P _h at this time is P ₁ .

As a result, the incident light power P is replaced with the difference (P ₀ -P ₁ ) of the heater power P _h , and the incident light power P can be known by knowing P ₀ and P ₁ . These relationships are given by P = K (P ₀ −P ₁ ). K is a calibration coefficient.

Next, the characteristic portion of the prior art will be described with reference to FIGS. 7 and 8. In FIG. 7, a constant current source 21 is connected to the thermoelectric cooling element. The output signal of the temperature difference detecting element is connected to the preamplifier 22, amplified to an appropriate size, and then input to the PID amplifier 23. The output signal of the PID amplifier 23 is amplified by the power amplifier 24 to drive the heater. The voltage across the heater is connected to a voltmeter 27. The controller 25 sets the current of the constant current source 21, controls the PID amplifier 23, reads the measured value from the voltmeter 27, etc., performs the calculation based on them, and displays it on the display unit 26. The key input unit 28 sets conditions for measurement. Reference numeral 29 is a memory in which the time constant of the light receiving head A is measured and recorded in advance. The controller 25 reads the information in the memory 29 when the power is turned on, and
The programmable attenuator 36 in the ID amplifier 23 is set.

FIG. 8 is a circuit diagram of the PID amplifier 23 shown in FIG. In FIG. 8, 31 is an input terminal, which is connected to the input terminal of the gain switching amplifier 32. The output terminal of the gain switching amplifier 32 has a proportional amplifier (P) 33, a differential amplifier (D) 34 and a programmable attenuator 3
An integrating amplifier (I) 35 is connected in parallel via 6. The output terminals of each of the amplifiers 33 to 35 are connected to the input terminal of the adding amplifier 37, and the output terminal of the adding amplifier 37 is connected to the output terminal 38. Reference numeral 39 is a control line of the programmable attenuator 36.

Here, the programmable attenuator 36
The output V ₂ of the integration amplifier 35 is obtained as follows, where D is the attenuation rate of R, R is the resistance of the integration amplifier 35, and C is the capacitance connected to the integration amplifier 35.

V ₁ = DV ₀ I = V ₁ / R V ₂ = − (1 / C) ∫Idt = − (D / CR) ∫V ₀ dt Therefore, the output V ₂ of the integrating amplifier 35 is the time constant CR. / D
Therefore, V ₀ is integrated.

Therefore, by setting the unique constant D of the light receiving head A, the PID control of the critical braking can be executed under the optimum condition.

[0023]

By the way, the time T required for measurement is T = 2 (T _c , where T _{c is} the time required for isothermal control and T _s is the time required for measuring the heater power P _h. + T _s ). Here, the reason for doubling is that it is necessary to open and close the shutter.

FIG. 11 is an explanatory diagram of these time relationships. In the specific example, the time T _c required for the isothermal control is 20 se.
about c, time T required to measure the heater power P _{h
Although s} varies greatly depending on the measured power level and the required accuracy, it is 0.5 sec to 1 sec at the 1 mW level.
That is, in this case, the measurement time T is 41 sec to 42 s.
ec, but most of the time is occupied by the time _Tc required for isothermal control.

The present invention has been made in view of the above problems, and an object thereof is to provide an isothermal control type calorimeter capable of shortening the total measurement time by shortening the time required for isothermal control. It is in.

[0026]

SUMMARY OF THE INVENTION The present invention which solves the above-described problems is directed to a light detecting portion in which a light absorber, a heater, a cooling means and a temperature detecting element are covered with a heat insulating jacket, and a temperature from the temperature detecting element. Incident light power calculation that calculates the incident light power from the difference in the power applied to the heater depending on the presence or absence of incident light, as well as the control unit that controls the heater to keep the temperature of the light detection unit constant based on the detection signal In the isothermal control calorimeter including a main body having means, the gain of the control unit is changed according to the presence or absence of incident light or the magnitude of control deviation.

[0027]

When the power greatly changes, the system convergence time is shortened by increasing the gain in the range where the system does not oscillate, and the noise is reduced by decreasing the gain in the range where the system does not become unstable during measurement.

In this way, the time required for isothermal control can be shortened, and the total measurement time can be shortened.

[0029]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a circuit diagram of an embodiment of an isothermal control type calorimeter according to the present invention, FIG. 2 is a circuit diagram of a PID amplifier used in FIG. 1, and parts common to those in FIGS. Therefore, re-explanation of them will be omitted.

In FIG. 1, reference numeral 40 is a comparator, the output signal of the preamplifier 22 is input to the comparator 40, and the output signal of the comparator 40 is input to the controller 25. The comparator 40 detects that the control deviation becomes zero based on the output signal of the preamplifier 22 and outputs the result to the controller 25.

In FIG. 2, the programmable attenuator 36 of the prior art is omitted, and the gain of the gain switching amplifier 32 is controlled by the controller 25.

In such a configuration, if the gain is increased within a range in which the system does not oscillate when the power greatly changes, the system converges quickly. In addition, noise can be reduced by lowering the gain within the range where the system does not become unstable during measurement.

Therefore, by increasing the gain during the interruption of the optical input and decreasing the gain during the measurement,
The isothermal control time is shortened. 3A and 3B are timing charts for explaining the operation when the shutter F is opened. FIG. 3A shows a change in gain, FIG. 3B shows a change in heater power, and FIG. 3C shows a change in control deviation. ..

Immediately before opening the shutter F, the PID amplifier 2
The gain of 3 is increased from the normal gain G1 to G2. Open the shutter F.

Since the isothermal control system is always operating, the control deviation which once becomes large gradually becomes small and crosses zero. The comparator 40 detects that the control deviation becomes zero. The signal from the comparator 40 lowers the gain of the PID amplifier from G2 to G1.

The heater power is measured. 4 and 5 are explanatory diagrams of simulation results by an electric circuit, and FIG. 4 shows a case where gain switching is not performed,
FIG. 5 shows a case where the gain is increased 10 times before opening the shutter F and the gain is returned to the original value when the control deviation becomes zero.

In FIG. 4, it takes 17.7 seconds until the heater power is completely converged, but in FIG. 5, it is 8.8.
It converges in sec. That is, the time required for the heater power to converge and the control time can be reduced to about 1/2.

As a result, the measuring time of the isothermal control type calorimeter can be reduced to about 1/2. The timing of the PID gain increase / decrease control is not limited to that in the embodiment. That is, the gain increasing timing may be the same as the opening / closing of the shutter, and the gain reducing timing may not be the timing at which the control deviation crosses zero. In particular, by configuring the controller to control the timing of gain reduction after a certain period of time from opening / closing of the shutter, the comparator becomes unnecessary and the cost can be reduced.

[0039]

As described in detail above, according to the present invention, the following effects can be obtained. That is, when the power of the incident light changes greatly, the gain of the control unit is increased in the range where the system does not oscillate to shorten the convergence time of the system. Since the temperature is lowered, the time required for isothermal control can be shortened and the total measurement time can be shortened.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an isothermal control type calorimeter according to the present invention.

FIG. 2 is a circuit diagram of a PID amplifier used in FIG.

FIG. 3 is a timing chart illustrating the operation of FIG.

FIG. 4 is an explanatory diagram of a simulation result by an electric circuit.

FIG. 5 is an explanatory diagram of a simulation result by an electric circuit.

FIG. 6 is a configuration diagram of a known isothermal control type calorimeter.

FIG. 7 is a circuit diagram of a prior example of a PID-controlled isothermal control type calorimeter.

8 is a circuit diagram of a PID amplifier used in FIG.

9 is an explanatory diagram of a measurement state of the configuration of FIG.

10 is a timing chart illustrating the operation of FIG.

11 is an explanatory diagram of a time relationship associated with opening and closing of the shutter having the configuration of FIG.

[Explanation of symbols]

 A light receiving head B main body F shutter S sensor section 1 heat absorber 4 heater 6,6a temperature difference detecting element 7 thermoelectric cooling element 8 reference jacket 23 PID amplifier 25 controller 40 comparator

Claims (1)

[Claims] 1. A light detecting section in which a light absorber, a heater, a cooling means, and a temperature detecting element are covered with a heat insulating jacket, and a heater is driven based on a temperature detection signal from the temperature detecting element to drive the temperature of the light detecting section. In the isothermal control type calorimeter, which comprises a control unit for controlling so as to keep constant, and a main body unit having an incident light power calculation means for calculating incident light power from the difference between the presence and absence of incident light in the electric power applied to the heater, An isothermal control type calorimeter, wherein the gain of the control unit is changed according to the presence or absence of incident light or the magnitude of control deviation.